1. Field of the Invention
The present invention relates to a two-step method for the production of a low-viscosity, water-soluble polymeric dispersion containing at least one polymeric dispersing agent (D) and a polymer (A) consisting of (a1) at least one water-soluble monomer, (a2) at least one hydrophobic monomer and, if necessary, (a3) at least one amphiphilic monomer.
2. Discussion of the Background
Aqueous dispersions of water-soluble polymers are used, for example, as a flocculent in the treatment of wastewater, as a dehydrating agent after the aqueous phase is separated, as a retention agent in paper production, as a soil improvement agent or as a dispersing agent.
EP 170 394 describes a liquid which can be mixed with water. This liquid consists of particles which are composed of a high-molecular polymeric gel with particle sizes greater than 20 .mu.m in an aqueous solution. The continuous phase is an aqueous solution which contains an equilibrium agent which keeps the water content of the gel particles in equilibrium with the water portion in the continuous phase and thus prevents agglomeration of the gel particles. Preferred equilibrium agents are the sodium salt of polyacrylic acid or polydiallyldimethylammonium chloride (Poly-DADMAC).
EP 183 466 describes a method for the production of a water-soluble polymeric dispersion in which a water-soluble monomer is polymerized while stirring therein at least one salt in the presence of a dispersing agent in an aqueous solution. Polyhydric alcohols, polyalkylene ethers, alkali salts of polyacrylic acid and alkali salts of poly-2-acrylamido-2-methylpropane sulfonic acid are used as dispersing agents or salts, which do not solvate the polymer in aqueous solution.
DE-PS 29 24 663 describes a method for the production of an aqueous dispersion from a water-soluble polymer substance having good stability and flowability. The water-soluble polymer contains at least one water-soluble ethylenically unsaturated monomer. A polyalkylene ether, polyethylenimine or the like can be used as a dispersing agent, if necessary, in the presence of inorganic salts. The aqueous dispersion produced in this way can be used, if necessary after it is diluted with water, as a flocculent aid, a thickening agent, a soil conditioning agent, and in other applications.
JP Kokkai 59 108 074 describes thickening agents which consist of polymers in aqueous solution which contain (meth)acrylic acid and/or their salts, (meth)acrylic amides, as well as methyl or ethyl acrylate as monomeric components, with polyethyleneglycol as dispersing agent.
German patent application P 42 16 167.3 describes aqueous dispersions of water-soluble polymers which are produced by polymerization of a mixture consisting of water-soluble, hydrophobic and if necessary amphiphilic monomers in the presence of a polymeric dispersing agent.
The aqueous solutions described in EP 170 394, which contain gel particles, have the disadvantage that they have elevated viscosities after a longer static period. The viscosity can only be lowered by the application of shear forces such as by stirring. The characteristics of the liquid depend on a complex equilibrium between polymer, equilibrium agent, water content and particle size of the gel particles.
In EP 183 466 water-soluble polymers, with the help of a dispersing agent, are used as dispersions in aqueous saline solutions. The disadvantage of these dispersions is the high salt content of the aqueous phase (up to 30 weight %) in comparison to a relatively low polymer (active ingredient) content (up to 20 weight %), which can lead to wastewater problems in certain applications of such dispersions.
A negative effect of the use of aqueous dispersions described in DE-PS 29 24 663 is the high number of parts of dispersing agents relative to the water-soluble polymer. If the above mentioned dispersion is used as a flocculent for (electrically) charged parts, for example, the active ingredient on high-molecular ionic polymers is reduced by the comparatively low-molecular dispersing agent.
The polymers which have a thickening effect produced in accordance with JP Kokkai 59 108 075 have an average molecular weight M.sub.W between 10.sup.5 and 5.times.10.sup.5 Dalton (mean weight), which is considerably too low for use as a flocculent.
The task to produce aqueous dispersions of water-soluble polymers with low viscosity, a high polymer active ingredient content, a high polymer molecular weight and a salt-free aqueous phase, which results from the above mentioned state of the art, is accomplished by the invention's polymers in aqueous dispersion in accordance with P 42 16 167.3. However, within the parameters of viscosity of the aqueous dispersion, high content of polymer active ingredient and high polymer molecular weight, a need continues to exist for such aqueous polymer dispersions of low-viscosity.